Carbon coating layers have been found to improve the catalytic performance of transition metals, which is usually explained as an outcome of electronic synergistic effect. Herein we reveal that the defective graphitic carbon, with a unique interlayer gap of 0.342 nm, can be a highly selective natural molecular sieve. It allows efficient diffusion of hydrogen molecules or radicals both along the in‐plane and out‐of‐plane direction, but sterically hinders the diffusion of molecules with larger kinetic diameter (e.g., CO and O2) along the in‐plane direction. As a result, poisonous species lager than 0.342 nm are sieved out, even when their adsorption on the metal is thermodynamically strong; at the same time, the interaction between H2 and the metal is not affected. This natural molecular sieve provides a very chance for constructing robust metal catalysts for hydrogen‐relevant processes, which are more tolerant to chemical or electrochemical oxidation or CO‐relevant poisoning. With interlayer gap of 0.342 nm, graphite armor serves as a natural molecule sieve screening out bulky adversative molecules like O2 or CO but allowing H2 to diffuse along both the out‐of‐plane and in‐plane direction. This creates perfect chance for fabricating robust HOR electrocatalysts.